Exogenous GABA is quickly metabolized to succinic acid and fed into the plant TCA cycle.

Exogenous application of γ-aminobutyric acid (GABA) could improve plant tolerance to environmental stresses such as hypoxia, heat, cold, drought, and salt stress. However, the mechanism by which GABA relieves stress is poorly understood. Here, we studied the uptake and metabolism of exogenous GABA in citrus leaves. Leaves were incubated in GABA solutions and the levels of endogenous GABA, succinic acid, and fumaric acid were investigated. Interestingly, the levels of endogenous GABA, succinic acid, and fumaric acid were quickly increased in GABA-treated leaves. This result indicated that GABA was taken up by the leaf, metabolized to succinic acid, and fed into the tricarboxylic acid cycle (TCA). This finding suggested that exogenous GABA could enhance plant resistance to biotic and abiotic stresses by generating more energy through the activation of the GABA shunt pathway and TCA cycle.